Don't pass along unused btStackAlloc everywhere. The API change might user code (derived classes with the old virtual method are not called anymore)

src/BulletCollision/CollisionDispatch/btCollisionWorld.h

@@ -65,7 +65,6 @@ subject to the following restrictions:
 #ifndef BT_COLLISION_WORLD_H
 #define BT_COLLISION_WORLD_H
 
-class btStackAlloc;
 class btCollisionShape;
 class btConvexShape;
 class btBroadphaseInterface;
@@ -91,8 +90,6 @@ protected:
 
 	btDispatcherInfo	m_dispatchInfo;
 
-	btStackAlloc*	m_stackAlloc;
-
 	btBroadphaseInterface*	m_broadphasePairCache;
 
 	btIDebugDraw*	m_debugDrawer;